1. Field of the Invention
The present invention relates to a numerical control (NC) machine tool apparatus, more particularly, to a computerized numerical control (CNC) machine tool apparatus having a means for automatically producing an NC work program used therein for machining a workpiece, on the basis of a source NC program.
2. Description of the Related Art
When machining workpiece by a CNC machine tool apparatus, which includes a plurality of spindles, drive mechanisms thereof and a control unit, an NC work program is previously programmed on the basis of parameters describing a machining shape of a workpiece to be machined, machining directions, a speed at which a tool is to be moved and other machining conditions. The programmed NC work program is loaded into a memory of the control unit. Thereafter, the control unit drives the drive mechanisms in accordance with the loaded NC work program to thereby machine the workpiece by the tool mounted on the spindle.
Various methods of programming an NC work program have been adopted, however, these methods suffer from the following disadvantages related to typical prior art programming methods.
When a machining shape of the workpiece is simple, a theoretical calculation method has been attempted. In this method, a skilled programmer or designer calculates a machining shape of the workpiece theoretically, programs a source NC work program represented by an NC language, and loads the source NC work program into a programming computer. The theoretical calculation method is different from an NC machine tool apparatus in which the workpiece is machined to produce an NC work program by, for example, an NC work programed paper tape. The NC work program is tested and loaded into the NC machine tool apparatus via a paper tape. This theoretical calculation method, however, requires skilled programmers, a programming computer for assembling a source NC work program and outputting an actual NC work programmed tape, and requires a long time for the programming.
A measuring method has also been attempted. In this method, an operator operates an NC machine tool apparatus in which a touch sensor, instead of a tool, is attached to a spindle. The touch sensor and measures a machining shape of the workpiece to be machined by the touch sensor. The programmer programs a source NC work program represented by an NC language on the basis of the measured data, and produces an NC work program. This measuring method also suffers from the disadvantages of the need for skilled engineers, a programming computer and a long programming time.
Furthermore, an Interactive programming method, in which an NC work program is produced interactively between a computer and an operator, has been attempted. This method does not require skilled engineers, however, does require a complex and bulky computer system and a long programming time.
Usually, a test operation of the NC work program loaded in the NC machine tool apparatus is attempted before actual machining of a workpiece. If an error of the NC work program is detected, a reprogramming operation must be carried out, and thus programming time becomes even longer, i.e., the efficiency of the programming is further lowered.
In addition to the above disadvantages, in the prior art programming methods, an NC work program must be produced for each machined shape of a workpiece. For example, when a modification is made to a machined shape, slightly different from a source machined shape, a new NC work program must be produced.